Vehicles have been developed to perform an idle-stop when idle-stop conditions are met and automatically restart the engine when restart conditions are met. Such idle-stop systems enable fuel savings, reduction in exhaust emissions, reduction in noise, and the like. As such, a number of methods may be used to control the transmission to improve idle-stops and subsequent restarts, when restart conditions are met.
One such example is illustrated by Suzuki et al. in U.S. Pat. No. 6,556,910 B2. Therein, a plurality of transmission forward clutches are controlled by a hydraulic servo to shift the clutches between engaged and disengaged states when adjusting between idle-stop and restart conditions. Specifically, when an idle-stop condition is satisfied, the transmission is maintained in gear and a hydraulic pressure of the hydraulic servo is also maintained at a predetermined pressure.
However, the inventors have recognized several potential issues with such a method. As one example, during idle-stop conditions, the time required to stop the engine, for example the time required to drop the engine speed from 700 RPM to zero, may be longer than desired. As such, if the time needed for engine shut-down is too long, a vehicle operator may choose to restart and/or launch the vehicle before the engine speed has dropped to zero.
Thus in one example, some of the above issues may be addressed by a method of controlling a system including an engine that is selectively shut-down during engine idle-stop conditions, the system further including a hydraulically actuated transmission component. The method may comprise, during an idle-stop engine shut-down, adjusting a hydraulic actuation of the transmission component to adjust a drag torque on the engine to stop the engine.
In one example, the transmission component is a transmission forward clutch. Herein, the drag torque may be increased by increasing the hydraulic pressure supplied to the transmission forward clutch, thereby enabling adjustment of a drag torque to counteract rotation of the engine by the ground through the wheels/powertrain. An electric pump and/or accumulator system may also be used in addition to a transmission mechanical pump to provide sufficient hydraulic line pressure during the engine spin down. By supplementing a transmission mechanical pump with an electric pump, the net pumping capacity and consequently the net hydraulic line pressure supplied may be significantly increased or maintained during the shut-down, thereby enabling the powertrain drag torque to be applied to the engine, thereby providing a faster engine shut-down. In addition to enabling a faster engine shut-down, crankshaft oscillations due to cylinder air-spring effects after the engine speed had reached zero, may be significantly dampened. In an alternate example, the transmission component may be a torque converter lock-up clutch.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.